This invention relates to a process for imidizing vinyl-aromatic copolymers, in particular styrene copolymers, containing maleic anhydride.
The vinyl-anhydride copolymers containing maleic anhydride are known from U.S. Pat. No. 3,954,722. Said copolymers may be processed under heat, but, when they are mixed together at a high temperature with other polymeric products (with a view of obtaining, for example, an impact-or shock-resistant material), there are observed decomposition reactions as well as the formation of superficial blisters and cross-linkings. The process becomes thus extremely difficult and the superficial aspect of the products thus obtained is unacceptable.
When the maleic anhydride is replaced by the corresponding imide, as described in British Patent No. 1, 185, 544, the above-mentioned drawbacks disappear. Nonetheless, the use of maleic imide as a co-monomer involves some drawbacks inasmuch as the maleic imide is not easily to be found and its synthesis is laborious and rather complex.
It is also known from U.S. Pat. Nos. 3,651,171; 3,840,499; and 4,381,373 and from German Patent No. 3,430,802 to carry out the imidization of the preformed styrene-maleic anhydride copolymer with primary amines, if desired in the presence of water. Moreover, U.S. Pat. No. 4,404,322 teaches that the imidization with amines may be carried out either in the molten state or in organic solvents.